1. Field of the Invention
The present invention relates to material handling in general, and specifically to conveyor systems, and still more specifically to pneumatically operated anti-friction pop-up ball transfers and anti-skid plunger pads.
2. Background
Roller-type and belt conveyors are based on a design where the load conveyed travels in an essentially linear manner. Conventional conveyors utilize rollers or skate wheels, where the direction of transit on the conveyor is perpendicular to the axes of rotation of the rollers. Other conveyors utilize belts, which are driven by rollers at either end. Roller conveyors may be powered, gravity feed, or passive, where a person can manually move the load to be conveyed. Belt conveyors are usually powered. Conventional conveyors are adequate in most cases from a material-handling standpoint, for example when the conveyed load is being simply transferred from one point to another, or where the load does not need to be reoriented, repositioned or transferred from the conveyor.
Roller-type and belt conveyors, due to their linear-transit design, have shortcomings where a load needs to be reoriented, held stationary, or taken out of the conveyance stream. An example is where the conveyor connects multiple stations of an assembly area. A single roller-type or belt conveyor can be used to bring work-in-process to multiple work benches, each bench responsible for similar or different processing. Another example is where the work-in-process needs to be worked on while situated on a roller-type conveyor, where it is difficult to hold the work-in-process stationary on the rollers. In such cases, ball transfers and/or anti-skid plungers have been successfully used to provide a means for easily maneuvering loads, or holding them steady for processing. Ball transfers and plunger pads have been used to convert a simple conveyor into a progressive assembly line.
The operation of the ball transfer is relatively simple. The transfers are essentially a series of primary ball bearings that are individually supported by a manifold that is positioned along a conveyor path. When integrated with a conveyor track, the ball transfer units are typically arranged in a strip or a supporting plate which is secured across the side rails of a conveyor track. In a roller-type conveyor, the primary ball of the transfers can be in a retracted position within their housings, such that the balls do not extend above the rollers of the conveyor. When extended, the balls rise to a plane above the rollers, such that any load located over the ball transfer is now resting on the balls, above the conveyor rollers. The load may then be freely moved about in two dimensions, allowing it to be reoriented, aligned, or diverted to a track, bench or cart branching off the main conveyor, etc. Ball transfers are also used with belt conveyors, for example where plural belts driven by a single end roller are joined at their endpoint by pop-up transfers. Plungers are employed in a similar manner, for use in stably elevating a load.
Pop-up ball transfers and anti-skid plungers are not limited to use within a conveyor path or track. The transfers may be recess-mounted into a flush work surface, such as a table or bench top, such that a load may be maneuvered into a desired position when the balls are extended. Lowering the balls into the recesses then brings the load into stable contact with the table or bench top for processing, inspection, storage, and the like. Anti-skid pop-up plungers can also be used to stably hold the work while processing is performed, for example as a companion to fixed balls and/or rollers mounted on a work surface, or in a roller or skate-wheel style or belt type conveyor.
Pop-up ball transfers in particular have also been mounted on or recessed into the surfaces of mobile or stationary scissor-lifts, transfer carts, utility carts, etc. With the balls extended, a load may be maneuvered onto the cart from an adjoining conveyor or ball transfer module. When the balls are retracted into the surface, the load may be safely and stably transported. Similarly, anti-skid pop-up plungers can also be used to stably hold the work while processing is performed, or for elevating a load in a stable fashion above fixed balls or skate wheels mounted in the surface of the cart. Pop-up plungers can also be used as a companion to pop-up ball transfers.
The potential uses for pop-up ball transfers and anti-skid plungers are, as can be seen, very numerous. Because the number of possible arrangements of material handling and conveyor systems is virtually infinite, all the possible uses for ball transfer and anti-skid plunger stations, carts, benches, tables, inclines, etc., are impossible to catalog here.
A single prior art ball transfer unit 100, as described in U.S. Pat. No. 4,732,490, the contents of which are incorporated herein by reference, is depicted in FIG. 1. In use, this unit would be "ganged" with other ball transfer units arranged in a strip or array. The anti-friction element comprises a main body 101, having a tubular portion 113 with a small first bore 102 entering from a top surface 103. The main body consists of a tubular portion 114 with a second bore 104 extending through it. This tubular portion is closed at one end by the top wall 111 and closed at the other end by a bottom wall 112. The top wall has the first bore 102 extending through it and opening on its outer surface 103. The top wall has an integral tubular portion 113 extending from its inner surface having a bore which is an extension of the small bore 102. A piston 105 is slidable in the large bore 104 and has a cylindrical stem 106 which is slidable in the small bore 102. A primary ball 107 is rotatably mounted in the stem 106 concentrically of the small bore and resides in a cavity 108 formed in the stem. A coil spring 110 extends between the end of the tubular portion 113 of the top wall and a facing surface of the piston 105. A connector 109 is provided for introducing pressure air into the main body between the bottom wall 112 and the piston 105 to move the piston, so that the ball protrudes out of the small bore.
The piston 105 and the stem 106 are integral and the stem and the piston have the same cylindrical outer surface. The piston has two spaced radial flanges 119 and 120 between which lies a U-type seal 121 whose flexible element engages the surface of the second bore 104.
One disadvantage with the prior art design is that the tubular portion 113, after many cycles of pressurization of the transfer, may become loosened from the main body 101. Under pressure or a gas admitted through the connector 109 or under force from the spring 110, the piston and/or the tubular portion 113 may be forcefully ejected from the main body 101, causing injury or damage to inventory.
A further disadvantage with the prior art design is that the machining of the piston 105 with flanges 119 and 120 to receive the seal 121 is labor intensive and therefore costly. As the piston is machined on a screw machine, excessive tolerances may be introduced into the dimensions of the parts.